Antenna system



April 30, 1940.

W. L. EVERITT ANTENNA SYSTEM Filed Jan. 2'7, 1959 2 Shee'ts-Sheet -1 FROM TRANS/V/fftl? INVENTOR. 20. Q. {awe XXX BY &

ATT'oRNEY April 30, 1940.

w. L. EVERITT ANTENNA SYSTEM Filed Jain. 27, 1959 2 sheets-sheet 2 R m n N M m W. 3 3 C0 O W M E B m n m L v A 4 m a R Q I P. 4/ mm f 5: IR,

Patented Apr. 30, 1940 UNITED STATES PATENT OFFICE ANTENNA SYSTEM Application January 2'1, 1939, Serial No. 253,192

18 Claims.

My invention relates broadly to antennae systerns and more particularly to a circuit arrangement for an antenna array.

This application is a continuation-in-part of my copending application Serial No. 43,764, originally filed October 5, 1935, for Antenna system.

One of the objects of my invention is to provide a circuit arrangement for an antenna array having means for independently adjusting the current in each antenna of the array.

Another object of my invention is to provide a circuit arrangement for an antenna array having coupling means between the separate antennae by which the individual currents in the separate antennae may be controlled.

Still another object of my invention is to provide a circuit arrangement for antennae array for balancing the separate antennas by control of the phase and magnitude of the current in the separate antennas.

A further object of my invention is to provide a circuit arrangement for antennae array having means interconnecting the transmitter with the separate antennas by which desired delay may be introduced in the phase of the current supplied to one antenna with respect to the phase of the current supplied to another antenna.

A still further object of my invention is to provide means for balancing out the coupling due to the proximity of two or more antennae and adjusting the magnitude and phase of the currents in the antennae of an antenna array.

Still another object of my invention is to provide a link circuit coupling transmission lines feeding different antennae of an antenna array, and including means for eliminating mutual resistance as well as mutual reactance between the different antennae.

A still further object of my invention is to provide reactive and resistive elements in a link circuit coupling transmission lines feeding separate antennae of an antenna array for eliminating the entire mutual impedance between the antennae.

Other and further objects of my invention reside in the circuit arrangement for antennae array as set forth in the specification hereinafter following by reference to the accompanying drawings, in which:

Figure 1 diagrammatically illustrates one proposed circuit arrangement for the antennae array of my invention; Fig. 2 illustrates a modified form of circuit arrangement for antennae array embodying my invention; Fig. 3 is a schematic diagram of a modified form of the circuit arrangement illustrated in Fig. 1; Fig. 4 is a schematic diagram of the equivalent circuit of Fig. 3, indicating lumped elements as considered in the analysis of the circuit hereinafter set forth; Fig. 5 is a diagram of a portion of Fig. 4 with the inclusi on of a line component; and Fig. 6 is a diagram of a detail in Fig. 5 with the elements in rearranged positions.

In a system of transmission employing antennae array, difliculty has been encountered by reason of the fact that the current in one antenna induces a voltage in each of the other antennae or the array. This induced voltage modifies the apparent impedance in each of the coupled antennas. As a result, it becomes diflicult to make adjustments of current ratio involving both magnitude and phase. The coupling due to the proximity of two or more antennae is balanced out by a link circuit by adjustments of the magnitude and phase of the mutual impedance of the circuits interconnecting the antennae. I employ two or more antennae in the antennae array and connect each antenna with the high frequency transmission system through suitable transmission lines. I introduce a construction of delay circuit in one of the transmission lines and I introduce means for mutually coupling the transmission lines with adjustable circuit elements in both the delay means and in the coupling means for controlling the magnitude and phase of the current in each antenna. When adjustments are made for proper phase and magnitude of currents in each antenna, the mutual interaction of one antenna with respect to another is eliminated.

The mutual impedance between two antennas makes it diflicult to properly adjust the coupling networks connecting the antennas to the lines which deliver the power. A change in the magnitude or phase of the current in one antenna modifies the voltage induced in the other antenna and so changes the apparent impedance which the latter antenna presents to its coupling network. The efiect of this mutual impedance between the two antennas can be eliminated by circuits of the following general form.

Referring to the drawings in more detail, reference character I designates circuit connections from the output of a high frequency transmitter which includes an electrical circuit connection through output inductances 2 and 3 in series. Secondary inductances 4 and 5 are coupled respectively to the output inductances 2 and 3. Connections through transmission lines 6 and 'l are made to secondary inductances I and 5 through sets of coupling condensers indicated at 8 and 9 respectively. The transmission lines 6 and 1 may extend any practicable distance to the antennae array. For purposes 01' explainin my invention, I have shown two separate antennas in the antennae array but it is to be understood that the principles of my invention are applicable to antennae array of any desired number. I have represented one antenna system at l0 as comprising a doublet, but any type of antenna system may be employed. I have shown another antenna system at l2 consisting of another doublet. The doublet lli is excited from transmission line 6 through electrostatic coupling means l4 and transformer system it constituted by primary winding l6 and secondary windin l1. Coupling coils 8 and i9 are inserted in series between the ends of secondary winding IT" and the doublet In. A suitable ammeter is disposed in series with doublet ill to determine the magnitude of the current flow therein.

The connection of doublet H to transmission line is completed through a delay network which I have indicated generally by 2| as being constituted by sets of adjustable inductance elements 22 and 23 with a variable condenser connected therebetween indicated at 24. The transmission line connects through electrostatic coupling elements 25 with primary winding 26 of transformer 21, the secondary winding 28 of which connects to doublet l2 through inductance elements 29 and 30, as shown. The adjustable link circuit for interconnecting the transmission lines is represented at 3|, including coupling coil 32 adapted to be variably coupled with windings l8 and I9 and coupling coil 33 adapted to be variably coupled with windings 29 and 30. A tuning device 34 is disposed in the link circuit 3| in connection with the other elements in the link circuit. A suitable indicating meter 35 is provided in circuit with doublet l2 for indicating the magnitude of the current in the doublet.

Adjustment in current ratio with respect to both magnitude and phase in doublets ill and I2 may be made by adjustment of coupling coils 24 and 35. The adjustable elements of the delay network 2| and the variable elements in the link circuit 3| interconnecting the doublets are adjusted to efiect the desired phase relationship of the currents. The link circuit 3| is adjusted so that the coupling due to the antennae is balanced out by the link circuit.

The circuits of my invention in which the antennae are conjugate permit tests to be made of the field strength of the transmitter at a distance by first exciting one antenna then the other antenna and then both simultaneously for observing whether the currents are in proper phase.

,In the modified form of my invention shown in Fig. 2, the transmission line 6 is also provided with a delay network which I have indicated at 36 as including adjustable inductance elements 31 and 38 interconnected by variable condenser 39. In this form of my invention, the transmission line 6 includes inductance coils 40 while transmission line 1 includes inductance coils 4| and to these sets of inductance coils, I couple the link circuit shown at 42 including coupling coil 43 and coupling coil 44 connected through a variable condenser 45. Adjustment may be made of thelink circuit and of the elements in the delay networks 2| and 3B for determining the magnitude and phase relation of the currents in the'antennae which I have indicated at 46 and 41.

Transmission line 6 connects to opposite terminals of inductance element 48 in circuit with the antenna 46. Transmission line connects to opposite terminals of inductance element 49 in circuit with antenna 41. A suitable meter 50 is connected in circuit with antenna 46 and a suitable meter 5| connected with antenna 41 for indicating the magnitude of the current in each antenna.

A link circuit of the type shown in Fig. 1 by 3 I, and Fig. 2 by 42, which has no dissipative elements can only be used to eliminate the mutual reactance between the antennae and cannot affect the mutual resistance. A useful object is accomplished by eliminating this mutual reactance as in many cases it is the predominant form of coupling. If the link circuits also contain resistive elements, it is possible to eliminate the entire mutual impedance but at the expense of the power'which is dissipated in the resistive elements of the link circuit. This principle must be realized in order to make any adjustments on any antenna system containing a decoupling network.

In Fig. 3 I have shown the circuit of Fig. 1 in somewhat modified form; the principal distinction, however, is the provision of resistive elements 52 in the link circuit 3| the purpose and function of which will be understood from the following analysis of the principles involved. Tofacilitate the explanation, the equivalent circuit of Fig, 3 wherein all elements are lumped and represented in theoretical entities, will be considered. Fig. 4 shows the equivalent circuit of Fig. 3 and represents the voltage supplied to the antenna coupling circuit l5 at E1, and that to antenna coupling circuit 21 at E2, in accordance with Thevenins Theorem. Currents I1 and I2 are represented as flowing in the respective coupling circuits and antennae which have resistances R11 and R22 and reactances X11 and X22, both respectively. Impedance Z12, comprising reactance X1: and resistance R12, constitutes the mutual impedance between the antenna systems. The characteristics of the link circuit are similarly represented, X1: and X23 representing the coupling reactances to the respective antenna systems fed from E1 and E2, and Z3: the impedance of the link circuit comprising resistance R33 and reactance Xaa; the current in the link circuit is represented as Is.

The separate systems related through the mutual impedance Z1: will be termed antenna mesh A1 and antenna mesh A2, indicating the systems supplied from sources E1 and E2, respectively. The link circuit will be termed antenna decoupling mesh A3, with current I3 flowing therein, the function of this decoupling mesh A: being to counteract the detrimental coupling eflected by the mutual impedance Z12 between antenna meshes A1 and A2.

If the decoupling mesh is to serve its purpose, then the voltage induced by I1 in mesh A2 due to the mutual impedance Z1: must be equal and opposite to that induced in mesh A: due to the link circuit. In this case a current I1 will not tend to set up any current in mesh A2. By the reciprocity theorem, if this condition is achieved, a current I: will not tend to set up any current in mesh A1. The voltages induced in mesh A1 may be computed most conveniently by considering mesh A: as open circuited.

The voltage induced in mesh A: due to the mutual impedance Z1: will be The voltage induced in mesh A: by current in mesh A; will be 1 12112,; 211211-21; As explained, the condition for decoupling will be EIZHZM a: i Li N n aa 1a' n aam This gives as the necessary and sufllcient condition for decoupling,

Z12Zsa=Z13Z2a (3) Now Z1: and Z2: are pure reactances and may be'either of positive or negative sign. Hence Z12Zaa== (11x11) (:iXza) =iX1aX2a. (4)

The mutual impedance Z1; between two an- 5 tennas may lie in any of the four quadrants, i. e., its resistive component may be either positive or negative. On the other hand. Z3: must have a positive resistance. It Z1: has a positive resistance Eq. 4 can be satisfied by using the positive sign on its right hand side and making Z23 have an angle which is the negative of the angle of Z12. If Z12 has a negative resistance Eq. 4 is satisfied by using the negative sign on the right hand side and making the angle of Zn equal to 180 minus the angle of Z12.

Eq. 4 may be used to solve for the values of R33 and X13 required. Two cases must be considered.

Case I: R12 positive Let Z12=R12+7'X12 and Z3a=R3s+1Xam Then by Eq. 4

Z12Za3=R12R33-X12X33+ ;i(Ra3X12+R12X33) =X13X2a (5) Equate the reels and imaginaries:

R12R33-X12X33X13X23=0 (5a) m RasXu-i-RmXa: 0 (5b) Solve Eq. 50- for Rea:

X X X RJJ=XIZ 33g 18 23 i2 Solve Eq. 5b for Razz RHXBS 6b R3! X12 Equate Eqs. 6a and 6b and solve for Km:

I 12 1: |2 2a u Rn in IZIEP (7a) Substitute Eq. 7a in Eq. 6b:

- RUXZIXIH b aa If mesh A: is open and mesh A: is closed From Eqs 7a and 7b:

' Ea -lfiz uZaz-' ls I X11 X11 (8) EZDZ Hence, for this case, X1: must be the opposite 1:95 (1) type of reactance to X12.

As it is desirable to make the power dissipated in the link circuit a minimum, let the apparent impedance presented to the generator E1 be designated by the symbol Z11, and the apparent impedance presented to the generator E: be given the symbol Z22, where Now, due to the fact that there is no effective coupling between meshes l and 2,

and

By Eqs. 7a and 7b,

( ifl X122) ifl ll XISIXIQ and by making further use of Eq. 7b

a: n aa 23 1:

Insert Eq. 10 in Eqs. 9a and 9b:

l asl as+ 32 and en mwgfan (11b) The power delivered to the system by the two generators will be a m l l] l1"\"I 2l 22 may be picked to make this power delivered a minimum.

This minimum is obtained by differentiating Pdel. with respect to the ratio In the network it is assumed-that all resistances in mesh A1 and mesh A: are negligible, except those due to the antennas. Then the power delivered to the antennas is given by the relation which is welllmown for coupled circuits with mutual resistance:

Eq. 1'7 shows that if the currents I1 and I: are in phase with each other, there will be no power dissipated in the link circuit when the two antennas are being fed. During the process of adjustment the resistances presented to each generator will not be changed by changes in the opposite mesh, and their values are given by Eqs. 11a and 1117.

Case II: R1: negative The analysis for Case II where R12 is negative follows a similar reasoning. However Eq. 5a becomes This gives the following relations for this case: R (7c) X..=+ Z%; (7 R =R -%R (11c) R,,'=R,,-R,, (11d) (Note that in the above equation Ru itself is a negative number).

Eqs. 8 and 13 also apply to this case without modification.

In this case there will be no power dissipated in the link circuit when I1 and I: are in phase opposition.

Continuing with the general considerations, in operation the antennas will be separated in space and so the decoupling link will require a line with distributed constants to connect the mutual inductances adjacent to each antenna. When the decoupling adjustment is made and antenna mesh A1 is excited, the link circuit is effectively terminated .in an open circuit at the end coupled with antenna mesh A: since the voltage set up there does not produce any current. On a dissipationless line terminated in an open circuit the voltage does not shift phase along the line except at a voltage node where it reverses phase.

The decoupling link 3| of Fig. 3 is represented in Fig. 5. This is essentially the same as the decoupling circuit of Fig. 4 except that the line 53 has been added. However, the line 53 and the mutual -reactance"X:':'-canbe considered as a four-terminal coupling network in itself, the mutual impedance of which-will be shown to be a pure reactance. and will be termed the effective mutual reactance between the link circuit ti and antenna mesh A2. Its value for Fig. 3 may be determined by the same equations as determine X3: in the analysis of Fig. 4. The mutual impedance would be thevector voltage which appears between terminals tt-td when one ampere is sent into terminals tr-tz. It is easier to compute this if the network is reversed as shown in Fig. 6, and the mutual impedance is computed. as equal to the ratio Era/Is where L is the current supplied at terminals tit-t6. This is true because of the reciprocity theorem.

Assume that the line has the characteristic impedance and propagation constant of a dissipationless line with the following designations;

Then the input impedance at the terminals tat4 will be Zm.=Zo 00th 71 Let Xe be the reactance of the secondary circuit exclusive of the line, and Ib the current therein.

Then

The voltage Eu will be On an open circuited line the following relation applies:

g :=cosh -yl=cos 181 Therefore the effective mutual impedance of the four-terminal coupling network including Z0 and X13 1 be I X sin BZ-R cos Bl (18) Frequently, tuning reactances are inserted to reduce X to zero. In this case Eq. 18 reduces to j sa Zm=m (180) In either case, therefore, the effective mutual impedance is a pure reactance. This reactance should be of such a value as to fit the equations derived in the discussion of Fig. 4. Its magnitude can be controlled by any of the factors in Eq. 18 or 18a.

It is of importance to note that the length of the line does not affect the phase shift, with the possible exception of a phase reversal if the denominators of Eqs. 18 and 18a are negative. A phase reversal can be eliminated in this case by interchanging terminals t1 and in.

In Figs. 1-3 the elements shown are arranged to provide a balance to ground. It is customary to analyze circuits in which the balance is not given consideration. as was the case in the discussion of Fig. 4, and subsequently to rearrange the elements when a balance condition is necessary. The principles of accomplishing this are well known and need not be discussed here. In a similar way the circuits of my invention shown in Figs. 1-3 can be modified to take care of lines or antennas which are not balanced to ground.

Thus, it a resistive element is inserted in series in the decoupling system, as shown in Fig. 3, the

5' antenna systems can be completely decoupled.

The formula for the energy lost in the two'systerns under optimum-conditions of coupling when I the mutual resistance 01' the two antennas is positive is: iii

where R12 is the mutual resistance of the two antennas [Iil is the aboslute value of the current in antenna I r |I2| is the absolute value of the current in antenna 2 n U 0. is the phase angle between the two currents.

26 Hence if the mutual resistance is positive there will be no power dissipated in the decoupling link if either (a) I1 and I2 are in phase with'each other, or (b) The mutual resistance between the two antennas is zero.

I If the mutual resistance is negative the power dissipated in the decoupling link is Power lost=-2R12lIrHI2l(1'+cos (17a 30' In this case there will be no power dissipated ii I1 and I2 are in phase opposition.

The conditions for decoupling are that the effective resistance and reactance in the decou- '5' pling network shall be The upper signs are used when R1: is positive and the lower signs are used when R12 is negative.-

From' the above:

Therefore, the magnitude and phase oi the individual currents in each antenna maybe precisely controlled in accordance withfthe'principles of my invention so that one antenna does not tend to react upon another antennaoi an array, and the mutual resistance aswell as the "mutual reactance between the antennae is efiectively eliminated. I I

In the drawings I have illustrated my invention as applied to. doublets, but it is to be understood that my invention is equally applicable to radiating systems of various types and arrangezo ments.

While I have described my invention in certain of its preferred embodiments, I am aware that various modifications oi the circuit of my invention may be made and that I intend no limita- Power lost=2Ri2]IillI2](1- -cos a) (1'1) tions upon my invention'other' than are imposed by the scope of the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is as follows:

1. A transmission system comprising a source 5 of high frequency energy, a pair 01 doublet radiating systems, a pair of transmission systems connected with said source of high frequency energy, circuits interconnecting said transmission systems with each branch of said doublet radiating systems, a delay network disposed in one. oflsaid transmission systems, and a separate delay network interconnecting said circuits;

2. In a balanced antenna array employing a plurality of doublet antennae, in combination, means individual to each antenna for adjusting the phase and magnitude of the current in the respective antenna with respect to the currents in the other antennae, and means common to all antennae in said antenna array for compensat- 2 mg each antenna for the effects of the other antenna thereon, the last said. means being coupled with both branches of each of said doublet antennae.

3. In. a balanced antenna array employing a plurality of doublet antennae, in combination, means individual to selected antennae insaid antenna array for adjusting the phase and magnitude of the current in the respective antenna with respect to the currents in the other anten- I nae, and means common to all antennae in said antenna array for compensating each antenna for the efiects of the antennae thereon, the last said means being coupled with both branches of each of said doublet antennae.

4. In a balanced antenna array including a pair of doublet antennae, in combination, means individual to one antenna for adjusting the phase and magnitude of the current in said antenna with respect to the current in the other an- 40 tenna, and means common to both branches of each of said doublet antennae for compensating each antenna for the effects of the other antenna of said pair thereon.

5. In a balanced antenna array, a plurality of doublet antennae, means for compensating each antenna for the effects of currents in the other antennae which comprise an inductance element. in circuit with each branch of each doublet antenna, and a coupling link circuit including separate inductance elements coupled with those of the said inductance elements in circuit with the branches of individual doublet antennae, and a variable capacitance element connected with said separate inductance elements for adjusting the phase of the energy transferred through said coupling link.

6. In a balanced antenna array, a plurality of doublet antennae, means for compensating each antenna for the effects of currents in the other antennae which comprise an inductance element in circuit with each branch of each doublet antenna; and a coupling link circuit including separate inductance elements variably coupled with pairs of said inductance elements in cirg cuit with individual doublet antennae for ad- Justing the magnitude of energy transferred through said. coupling link circuit, and a variable capacitance element connected in said coupling link circuit for adjusting the phase of the energy transferred through said coupling link circuit.

7. In a balanced antenna array including a pair oi! doublet antennae, means for compensating each antenna for the eflects of currents in the other antenna which comprise an inductance element in circuit with each branch or each doubletantenna; and a coupling link circuit including separate inductance elements variablycoupled with pairs or said inductance elements in circuit with individual doublet antennae, and a variable capacitance element connected in parallel with said separate inductance elements in said link circuit.

8. In a balanced antenna array, a doublet antenna, a pair of transmission lines connected with said doublet, an inductance element. connectedin each transmission line, a separate, inductance element coupled with said inductance elements in common; a duplicate arrangementof antenna, transmission lines, and inductance elements; means including a condenser for interconnecting said separate inductance elements for forming a link coupling between said antennae;

;and other inductance elements connected with the transmission lines 01 at least one of said pairs, and a condenser connected across the transmission lines in cooperative relation with the last said inductance elements, for forming .a delay network for adjusting the phase and magnitude of current in the respective doublet antenna.

9. A transmission system comprising a source of high frequency energy, a pair of radiating systems, a pair of transmission systems connected with said source of high frequency energy, circuits interconnecting said transmission systems with said radiating systems, a delay network disposed in one of said transmission systems, and a separate network interconnecting said circuits.

10. In a balanced antenna array, a radiating system, a pair of transmission lines connected with said radiating system, an inductance element connected in each transmission line, a separate inductance element coupled with said inductance elements in common; a duplicate arrangement of radiating system, transmission lines, and inductance elements; means including 1 a condenser for interconnecting said separate inductance elements for forming a link coupling between said radiating systems and other inductance elements connected with the transmission lines of at least one of said pairs, and a con- .denser connected across the transmission lines in cooperative relation with the last said inductive elements, for forming a delay network for adjusting the phase and. magnitude of current in the respective radiating systems.

11. In a balanced antenna array including 'a pair or radiating systems, means for compensating each radiating system for the eflects of currents in 'the other radiating system, which comprise an inductance element in circuit with cuit including separate inductance elements variably coupled with pairs of said inductance elements in circuit with the respective radiating systems, and a variable capacitance element connected in parallel with said separate inductance elements in said link circuit.

12. An antenna system comprising a multiplicity of individual antennae, separate antenna coupling means connected with each antenna,

each radiating system; and a coupling link cirand means-interconnected with said coupling means and having a reactive characteristic for counteractingmutual reaction in said individual antennae anda resistive characteristic for counteracting mutual resistance in said individual; antennae, in operation.

13. -An antenna system comprising a multiplicity of individual antennae having separate coupling means for supplying energy thereto, and a decoupling link circuit interconnected with said coupling means and including means for counteracting mutual resistance and mutual reactance in said individual antennae in operation.

14. An antenna system comprising a multiplicity of individual antennae having separate coupling means for supplying energy thereto, said individual antennae being simultaneously energized and having mutual reactive and resistive characteristics, and means interconnected with said coupling means, and operative for counteracting the mutualreactance and resistance in said individual antennae.

15. An antenna system comprising a multiplicity of individual antennae having separate coupling means for supplying energy thereto, a single source of energy common to all said coupling means, means individually connected with selected ones of said coupling means for adjusting the phase and magnitude of the current in the respective antenna with respect to the currents in'the other antennae, and means common to all said coupling means for counteracting the mutual impedance in said individual antennae, the mutual impedance including mutual reactance and mutual resistance.

16. An antenna system comprising a multiplicity of individual antennae having separate coupling means for supplying energy thereto, said individual antennae being simultaneously energized and having mutual reactive and resistive characteristics, and a link circuit reactively coupled with selected ones of said coupling means and-including an energy dissipative element, said link circuit being operative to counteract the mutual reactance and resistance in said individual antennae.

1'7. An antenna system comprising a multiplicity of individual antennae having separate feeding means for supplying energy thereto, said individual antennae being simultaneously energized and'having mutual reactive and resistive characteristics," a resistance element, and means having 'a'substantially pure reactance character istic connected between said resistance elements and selected ones of said feeding means (or coupling said resistance element and the selected feeding means, said resistance element being effective to counteract the mutual resistance in the respective antennae and said reactive coupling means being cooperative through said resistance element'to counteract the mutual reactance in the 'respective antennae.

118.,An antenna system as set forth in claim 1'7 and including a transmission line in the said reactive coupling means, said line having a substantially'pure reactance characteristic as a por tion oi said reactive coupling means. 

